/* Copyright (C) 2000 MySQL AB & MySQL Finland AB & TCX DataKonsult AB

   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 2 of the License, or
   (at your option) any later version.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program; if not, write to the Free Software
   Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA */

/* functions on blocks; Keys and records are saved in blocks */

#include "heapdef.h"

/*
  Find record according to record-position.

  The record is located by factoring position number pos into (p_0, p_1, ...)
  such that
     pos = SUM_i(block->level_info[i].records_under_level * p_i)
  {p_0, p_1, ...} serve as indexes to descend the blocks tree.
*/

byte *hp_find_block(HP_BLOCK *block, ulong pos)
{
  reg1 int i;
  reg3 HP_PTRS *ptr; /* block base ptr */

  for (i = block->levels - 1, ptr = block->root; i > 0; i--)
  {
    ptr = (HP_PTRS *)ptr->blocks[pos / block->level_info[i].records_under_level];
    pos %= block->level_info[i].records_under_level;
  }
  return (byte *)ptr + pos * block->recbuffer;
}

/*
  Get one new block-of-records. Alloc ptr to block if needed
  SYNOPSIS
    hp_get_new_block()
      block             HP_BLOCK tree-like block
      alloc_length OUT  Amount of memory allocated from the heap

  Interrupts are stopped to allow ha_panic in interrupts
  RETURN
    0  OK
    1  Out of memory
*/

int hp_get_new_block(HP_BLOCK *block, ulong *alloc_length)
{
  reg1 uint i, j;
  HP_PTRS *root;

  for (i = 0; i < block->levels; i++)
    if (block->level_info[i].free_ptrs_in_block)
      break;

  /*
    Allocate space for leaf block plus space for upper level blocks up to
    first level that has a free slot to put the pointer.
    In some cases we actually allocate more then we need:
    Consider e.g. a situation where we have one level 1 block and one level 0
    block, the level 0 block is full and this function is called. We only
    need a leaf block in this case. Nevertheless, we will get here with i=1
    and will also allocate sizeof(HP_PTRS) for non-leaf block and will never
    use this space.
    This doesn't add much overhead - with current values of sizeof(HP_PTRS)
    and my_default_record_cache_size we get about 1/128 unused memory.
   */
  *alloc_length = sizeof(HP_PTRS) * i + block->records_in_block * block->recbuffer;
  if (!(root = (HP_PTRS *)my_malloc(*alloc_length, MYF(0))))
    return 1;

  if (i == 0)
  {
    block->levels = 1;
    block->root = block->level_info[0].last_blocks = root;
  }
  else
  {
    dont_break(); /* Dont allow SIGHUP or SIGINT */
    if ((uint)i == block->levels)
    {
      /* Adding a new level on top of the existing ones. */
      block->levels = i + 1;
      /*
        Use first allocated HP_PTRS as a top-level block. Put the current
        block tree into the first slot of a new top-level block.
      */
      block->level_info[i].free_ptrs_in_block = HP_PTRS_IN_NOD - 1;
      ((HP_PTRS **)root)[0] = block->root;
      block->root = block->level_info[i].last_blocks = root++;
    }
    /* Occupy the free slot we've found at level i */
    block->level_info[i].last_blocks->blocks[HP_PTRS_IN_NOD - block->level_info[i].free_ptrs_in_block--] = (byte *)root;

    /* Add a block subtree with each node having one left-most child */
    for (j = i - 1; j > 0; j--)
    {
      block->level_info[j].last_blocks = root++;
      block->level_info[j].last_blocks->blocks[0] = (byte *)root;
      block->level_info[j].free_ptrs_in_block = HP_PTRS_IN_NOD - 1;
    }

    /*
      root now points to last (block->records_in_block* block->recbuffer)
      allocated bytes. Use it as a leaf block.
    */
    block->level_info[0].last_blocks = root;
    allow_break(); /* Allow SIGHUP & SIGINT */
  }
  return 0;
}

/* free all blocks under level */

byte *hp_free_level(HP_BLOCK *block, uint level, HP_PTRS *pos, byte *last_pos)
{
  int i, max_pos;
  byte *next_ptr;

  if (level == 1)
    next_ptr = (byte *)pos + block->recbuffer;
  else
  {
    max_pos = (block->level_info[level - 1].last_blocks == pos)
                  ? HP_PTRS_IN_NOD - block->level_info[level - 1].free_ptrs_in_block
                  : HP_PTRS_IN_NOD;

    next_ptr = (byte *)(pos + 1);
    for (i = 0; i < max_pos; i++) next_ptr = hp_free_level(block, level - 1, (HP_PTRS *)pos->blocks[i], next_ptr);
  }
  if ((byte *)pos != last_pos)
  {
    my_free((gptr)pos, MYF(0));
    return last_pos;
  }
  return next_ptr; /* next memory position */
}
